1. Field of the Invention
The present invention relates to an information recording medium such as paper on which multimedia information including audio information of voice, music, etc., video information obtained from cameras, video equipment, etc., digital code data obtained from personal computers, wordprocessors, etc. is recorded as a two-dimensional code pattern which can be optically read, a two-dimensional code of the information recording medium, and a system and a method for optically reading the two-dimensional code pattern recorded on the information recording medium and reproducing the original multimedia information.
2. Description of the Related Art
Various recording mediums, such as magnetic tapes and optical disks, have been conventionally known as those for recording voice information, music information, etc. However, even though their reproductions are mass-produced, they increase in unit cost and require a very large space for keeping themselves. Furthermore, it takes time and trouble to transfer a recording medium on which voice information is recorded from one person to another far away therefrom, even though it is mailed or sent by hand. These problems are true of all the so-called multimedia information including video information obtained from cameras, video equipment, etc., digital code data obtained from personal computers, wordprocessors, etc., as well as audio information.
International Publication No. WO 94/08314 (corresponding to U.S. patent application Ser. No. 08/407,018) discloses a system capable of dealing with the above problems. According to this system, multimedia information containing at least one of audio information, video information and digital code data is recorded on an information recording medium, such as paper, in the form of a two-dimensional code formed by two-dimensionally arranging a plurality of dots, i.e., image information or encoded information which can be facsimiled and mass-produced at low cost, and it is reproduced therefrom.
In the system of the international publication, two-dimensional codes are optically read by holding an information reproduction apparatus and manually scanning the recording medium along the two-dimensional codes.
The structure of a two-dimensional code pattern is still being studied so as to improve in recording density. If higher density recording is achieved, the locations of respective dots of the two-dimensional code pattern have to be calculated with high precision. However, such high-precision calculation is not particularly taken into consideration by the above International Publication.
Jpn. Pat. Appln. KOKAI Publication No. 60-165503 discloses a method of reading information with high precision using a considerably large reference image. This method can be applied to a two-dimensional code as disclosed in the International Publication. If it is so, the following problem however will arise.
Assume that a marker is a circle with radius r composed of s dots, the size of a code to be read is a.times.b dots, and the size of one frame is c.times.d dots. If the real coordinates of the code is (i, j), the maximum tolerance for reading the code is (1.+-.a/2, j.+-.b/2). To keep effective precision, therefore, n.sub.x figures obtained by adding the number of figures indicating .+-.a/2 to those (c dots) indicating the X coordinate, are needed along the X-axis, and n.sub.y figures obtained by adding the number of figures representing .+-.b/2 to those (d dots) representing the Y coordinate, are done along the Y-axis. A larger one of n.sub.x and n.sub.y is therefore required on the whole.
For example, if the size of a code to be read is 3.4.times.3.4 dots and that of one frame is 500.times.500 dots, n.sub.x and N.sub.y are each five figures since three figures are required for defining the coordinates and two decimal places are required for representing an error. If the coordinates of s dots constituting the marker are (x.sub.i, y.sub.i) (i=1 to s), its centroid (g.sub.x, g.sub.y) is expressed as follows: ##EQU1## Therefore, the s dots have to be larger than a number in n.sub.x or n.sub.y figures. When the marker includes five figures dots (=ten thousand dots or more), the centroid of the marker can be detected. Since, in this case, .pi.r.sup.2 &gt;10000, the radius r of the marker is 57 dots or more. This marker, which is illustrated in FIG. 1, is very large and thus the recording density is remarkably decreased.